1. Field of Invention
The present invention relates generally to a low thread force two piece cable tie. More particularly, the invention relates to a locking device for such a cable tie that has an integral protruding tang serving as an anchoring device.
2. Description of Related Art
Plastic cable ties having metal locking device inserts are well known in the art. Examples of such include U.S. Pat. No. 3,457,598 to Mariani and U.S. Pat. No. 5,517,727 to Bernard et al.
Cable ties of this type include a metal locking device partially embedded at an angle within a strap accepting channel of a cable tie head. The metal locking device is situated at an angle that allows insertion of a cable tie strap in an insertion direction, but allows for engagement of the locking device with the strap when it is pulled in a removing direction to prevent removal. The metal locking device of such cable ties is in the form of a cantilevered beam that is fixed at one end and extends into the strap accepting channel at the free end. Operation of such a cable tie will be described with respect to FIGS. 1-3, which show operation of a cable tie device according to copending U.S. patent application Ser. No. 09/855,383, the subject matter of which is incorporated herein by reference in its entirety.
The cable tie 100 of FIG. 1 includes a strap 104 (partially shown) integral with a cable tie head 102. Cable tie head 102 is formed with a locking device receiving cavity 180 and a strap accepting channel 122 having a strap entrance 168 and a strap exit 166. Strap accepting channel 122 receives the leading end 112 of strap 104. Locking device receiving cavity 180 receives a pre-formed metal locking device 136, which is formed from a corrosion resistant metal such as stainless steel.
Locking device receiving cavity 180 is provided to allow access to the anchoring region on the end wall for partial embedding of metal locking device 136 in a mounting slot 130 of the cable tie head 102. Mounting slot 130 may be preformed in an interior surface of cavity 180 or may be partially formed as a result of pressing an end 134 of locking device 136 into the interior surface of cable head 102. This defines a cantilever beam structure having a fixed end 134 and a free end 138 that extends into strap accepting cavity 122. Metal locking device receiving cavity 180 also allows for movement of locking device 136.
As shown in FIG. 1, upon insertion of strap end 112 into the strap accepting channel, the free end of metal locking device 136 freely flexes due to the resiliency of the metal and the angle of the device to provide a low insertion force. Insertion of the cable tie strap continues to occur until strap 104 is sufficiently tight around an object to be constrained, such as an unshown cable bundle. Upon release of the strap, or through application of a withdrawal force on the strap, forces flex free end 138 of metal locking device 136 and cause a sharpened portion of free end 138 to begin to pierce strap 104 as shown in FIG. 2. When free end 138 sufficiently rests upon the fulcrum point 142, resistance to further withdrawal is attained up to a determinable tensile strength value, which is dependent on material selection and other variables.
Such a cable tie is sufficient for a single locking application (i.e., a single tightening operation). However, what occasionally happens is that after an initial tightening or attempt to withdraw the cable tie strap 104, a subsequent tightening or re-threading action may be initiated to further cinch down the cable tie. As the free end 138 of metal locking device 136 has already partially penetrated the surface of strap 104, it is possible that during these further re-thread attempts to advance the strap in the direction of exit 166, the free end will not break free from strap 104. Instead, the locking device 136 will remain partially embedded within the surface of strap 104. In such cases, if the retention force of the fixed end 134 is less than the withdrawal force necessary to break away free end 138 from strap 104, it is possible that fixed end 134 will be pulled out of slot 130. This is undesirable and results in cable tie failure as shown in FIG. 3, in which metal locking device 136 is either completely removed or sufficiently withdrawn from slot 130 to adversely affect proper cable tie functioning. In this example, the retention force acting on fixed end 134 to resist removal is the frictional force between fixed end 134 and slot 130. This retention force may be insufficient and is particularly problematic where the fixed end is oriented substantially parallel to the re-threading force acting on strap 104 toward exit 166, as in this example.
There is a need for a two-piece cable tie having an improved anchor retention system for a metal locking device.
There also is a need for a method of easily forming a barbed tang on a metal locking device of a cable tie to serve as an anchor.
It is an object of the invention to provide a two-piece cable tie with a locking device that has improved anchoring force to resist removal during initial and subsequent re-threading.
It also is an object of the invention to provide a method of forming a barbed tang on a metal locking device of a cable tie.
It is further an object of the invention to punch one or more tangs onto a metal locking device so as to form a ramp that is in a direction conducive to installation but provides resistance to attempts to withdraw the device.
The above and other objects are achieved by a cable tie having an anchored metal locking device, comprising: a strap including a first end and a free end; a locking head secured to the first end of the strap, the locking head defining a strap accepting channel in the head having a strap entry end and a strap exit end, the locking head further including a metal locking device receiving cavity adjacent to and open toward the strap exit end of the locking head, the locking head further including a mounting slot having an inner support wall, an outer support wall and a support slot communicating the mounting slot with the receiving cavity; and a metal locking device mounted through the metal locking device receiving cavity into the support cavity, the metal locking device having a free end positioned within the strap accepting channel and a fixed end having at least one bent tang protruding outwardly from a surface of the metal locking device. The fixed end having the at least one bent tang is insertable through the support slot. Upon such insertion, the inner support surface of the mounting slot resiliently urges at least a protruding edge of the at least one bent tang against the outer support surface to anchor the metal locking device within the mounting slot and resist withdrawal of the metal locking device in a direction towards the exit end of the strap accepting channel.
The invention also provides a method of forming a cable tie having an improved anchoring system comprising the steps of: forming a cable tie having a strap including a first end and a free end and a locking head secured to the first end of the strap, the locking head defining a strap accepting channel in the head having a strap entry end and a strap exit end, the locking head further including a metal locking device receiving cavity adjacent to and open toward the strap exit end of the locking head, the locking head further including a mounting slot having an inner support wall, an outer support wall and a support slot communicating the mounting slot with the receiving cavity; forming a metal locking device with a fixed end having at least one bent tang and a free end; initially mounting the metal locking device through the metal locking device receiving cavity into the mounting slot by inserting the fixed end through the support slot until the fixed end is urged against the inner support wall; and further inserting the metal locking device into the mounting slot and causing the inner support surface to be resiliently deformed until the at least one bent tang is substantially received within the mounting slot, at which time the inner support surface urges at least an edge of the at least one bent tang against the outer support surface to securely anchor the metal locking device to the mounting slot.